I have the following Holtz info in Amador County:

From the Poll List, Jackson Precinct, Township 1, Amador County:

John Jacob Holtz, age 35, Farmer, Naturalized Citizen, residing in Jackson, registered (to vote) on 9/19/1868.

Peter Holtz, age 35, Farmer, Naturalized Citizen, residing at Murphy's Ridge, registered (to vote) on 9/19/1868.

From the Great Register (of voters) Amador County, 1892:

Henry Holtz, age 28, height 5'11-1/2", complexion light, eyes gray, hair brown, farmer, born in California, Precinct S. Jackson, date of registration 9/23/1892.

I hope these are your people.

Deborah